Laminated food package



Sept. 20, 1966 H. CURLER ETAL LAMINATED FOOD PACKAGE Original Filed May 14, 1963 ffzveiz any Hawarai CurZer {Q i I 561222 E Lz'zzebacy United States Patent 3,274,004 LAMINATED FOOD PACKAGE Howard Curler and Glenn E. Lineburg, both of New London, Wis., assignors, by mesne assignments, to Curwood, Inc., a corporation of Delaware Original application May 14, 1963, Ser. No. 280,200. Divided and this application Apr. 21, 1964, Ser. No. 361,484

5 Claims. (Cl. 99171) This application is a division of our copending application, Serial No. 280,200, filed May 14, 1963, and the invention relates to a flexible wrapping material in laminate form and is particularly useful in wrapping food products although not limited to such use.

In the packaging of various food products, such as cheese and meat, in a flexible wrapper, difficulty has been experienced with the development of small pinholes in the wrapper at points of stress resulting from flexing of the wrapper during shipment and handling. This results in a loss of the essential barrier characteristics of the wrapper and permits loss or gain of moisture by the package and access of oxygen into the package, with consequent spoilage of the product intended to be protected by the wrapper.

In the so-called nonconforming type of flexible wrapping package, a bulk product, such as cheese or meat, is encompassed by the wrapping material along the side, top and bottom margins of the product, and the wrapping material extends a substantial distance beyond the ends of the product where the package is end-sealed after being gas-flushed with an inert gas such as nitrogen, carbon dioxide, or the like. The resultant package, therefore, has end portions which are subject to deformation, crinkling, wrinkling, and other flexing action caused by pressures of any kind that are applied against unsupported end portions of the package, and particularly end pressures such as occasioned in shipment of the package in a bulk shipping container. The continual flexing of the unsupported ends sooner or later causes pinholes to develop in the material, with the result that gas and vapor can pass through the wrapper and accelerate spoilage of the food product.

It should be understood that a conforming package, such as results from vacuum packaging, is also subject to pinhole development, although in this type of packaging, the problem is ordinarily not as severe, because the wrapper makes contact with, and is supported by the product.

Coated and laminated wrapping materials have been used in an effort to provide a proper combination of physical properties in a wrapping material to adequately protect the food product contained within the package, but none of the materials used for this purpose have satisfactorily solved the pinhole problem of nonconforming packages.

For example, a coated sheet has been used comprising a base material consisting of polyethylene terephthalate (commonly known as Mylar and sold by E. I. du Pont de Nemours & Co.) with the base material being exteriorly coated with vinylidene chloride copolymer (commonly known as Saran and sold by Dow Chemical Company of Midland, Michigan), and with the inside of the wrapping material having a polyethylene film used for its heat-sealing properties. Such a Wrapping material of this general type is sold, for example, under the trade designation MKP-SZOO and is made by Curwood, Inc. of New London, Wisconsin. Experience has taught, however, that this type of material, which is the best available for nonconforming food packaging, is still subject to pinhole cracking.

The present invention has, for its primary object, the

3,2?4fi04 Patented Sept. 20, 1966 solving of the pinhole problem, and the accomplishment of this result while still preserving in the food Wrapper the desirable and necessary physical properties of a satisfactory wrapping material.

A further object of the invention is to provide a wrapping material of this general classification which uses relatively inexpensive laminate materials; which is completely adaptable to present heat-sealing machines and equipment; which has appropriate barrier properties with respect to gases and vapors; and which, in addition to being substantially pinhole-proof, is also abrasionresistant.

Further and other objects of the invention will become apparent as the disclosure proceeds and the description is read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a perspective view showing a nonconforming package containing a food product, such as cheese, and showing the areas in which pinhole leaks are inclined to develop with prior art wrapping materials; and

FIGURE 2 is an enlarged cross-sectional view showing a preferred form of the laminate of this invention.

The wrapper of this invention may be used for the hand wrapping of a product, but ordinarily the wrapper is used on an automatic machine which forms and closes the package by means of heat sealing. Use of a thermoplastic material for the inner surface of the wrapper, and forming the package with a face-to-face relationship of this material, permits the formation of a heat-sealed closure which is gastight. With some products, such as cheese and meat, it is found advantageous to displace the air from the void space inside the package by flushing with an inert gas, or by evacuation, before sealing the package. The retention of this gas, or vacuum, and the substantial exclusion of the atmospheric oxygen, is important to the proper preservation of the product.

With many products, the dimensions of the package are such that it is necessary to provide an excess of wrapping material in order to bring the end portions of the wrapper together in a flat, face-to-face relationship, which is free of wrinkles that would give channels through the heat-sealed seam. Forcing the flat wrapper to enclose a rectangular product in this way gives rise to three-way creases which meet in a sharp point in the end portions of the package. As this excess portion of the Wrapper is flexed during handling and shipment, there is an accumulation of stresses at these points, or at any other point Where flexing has produced intersecting creases. The strength and flexibility of previously known and used wrappers has not been adequate to withstand these repeated concentrated stresses. This has resulted in the development of flex cracks and pinholes in the end portions of the wrapper, as shown at 9 in FIGURE 1, with consequent loss of the barrier properties of the wrapper, and failure of the package.

We have discovered a new and unique combination of sheet materials which, in a laminated construction, provides the required functional properties, and, in addition, gives the necessary resistance to flex cracking and pinholing to give a successful wrapper. This laminated wrapper consists essentially of the following components in the sequential order given:

(1) The interior layer of the lamination (i.e. the layer next to the product being wrapped) is a heat-scalable material, suitable for the product being packaged, as for example, polyethylene, as shown at 1.0 in FIGURE 2.

(2) The base material of the laminate is cellophane (a regenerated cellulose sheet material), as indicated at 11.

(3) The third essential layer is polyethylene, as indicated at 12.

(4) The fourth and outside layer, as indicated at 13, is a suitable high temperature, heat-resistant layer which has a melting point above that of the adjacent polyethylene.

Preferably the cellophane layer 11 is coated on at least one side and desirably on both sides with Saran, as indicated at 14 and Preferably, also, the exterior layer 13 is an oriented polypropylene, and more specifically a heat-set, biaxially oriented polypropylene film, although it may consist of Mylar, or any other suitable material having a higher melting point than the adjacent polyethylene layer and other requisite properties for a wrapping material. Preferably, also, the polyethylene has a density of from about 0.914 to about 0.925 and a melt index from about 4 to about 12.

We prefer to extrusion laminate the composite sheet, although glue lamination may be employed if desired. The reasons for the unexpected and exceptional performance of the preferred combination of materials, and the preferred extrusion coating process, with respect to resistance to flex cracking and pinhole development, is not fully understood. It is believed to be due in some way to the distribution of stresses and the interaction of the essential component layers of the lamination so as to deliver maximum performance of the wrapper.

As before stated, the most satisfactory wrapping material for nonconforming packages has been Mylar used as the base sheet with an inner polyethylene coating for sealing, but tests have shown it to be subject to objection because of flex cracking and pinhole development.

In our laminate, which uses relatively inexpensive materials, the cellophane provides a non-thermoplastic base layer which gives good performance over a broad range of sealing temperatures without burn-through, and has good strength and stretch resistance which is desirable; the Saran, if used, supplies a good barrier against the passage of gases and vapors; the inside polyethylene coating 10 also adds to the mosture barrier and, in addition, serves as a heat-sealing medium for package closure; the outer polyethylene coating or layer 12 again adds to the moisture barrier, but, more importantly, serves, with the inside polyethylene layer 10, to confine the cellophane layer 11 in sandwhich fashion, and thereby, through the flexible properties of the polyethylene, give physical interface support to the more brittle cellophane layer contained therebetween; and the exterior layer 13 serves the purpose of allowing the polyethylene-encased cellophane to be satisfactorily used in conventional heat-sealing machines, since it has a melting point above that of the adjacent polyethylene.

The oriented polypropylene film used for the outside layer 13, which oriented polypropylene is preferably heatset and biaxially oriented has the advantage of being tough, flexible, stretch-resistant, and resistant to surface abrasion, while also preventing sticking of the wrapper to the heat-sealing bars on the packaging machine.

Although the Wrapping material of this invention is particularly useful in conjunction with nonconforming packaging procedures, it should be understood that the material is also applicable to and useful in conjunction with vacuum packing and conforming wrappers.

The relative thickness of the composite layers of the laminate of this invention may, of course, vary within the limits which will be recognized by those skilled in the art, but, in general, it may be said that the composite thickness of the cellophane layer 11 with the flanking Saran layers, when used, may be on the order of .8 mil, the inside polyethylene coating 10 may be on the order of 1 /2 mils, the outside polyethylene coating 12 may be on the order of .5 mil, and the polypropylene coating 13 may be on the order of .5 mil.

Certain preferred embodiments of this invention and methods of making the laminate are illustrated in the following specific examples:

No. l: A film of 50 gauge, heat-set, biaxially oriented polypropylene, Moplefane OTT from Montecatini of Italy, was extrusion laminated to 250 RS l-E cellophane (Saran-coated) from American Viscose Corp., with five pounds, per 3000 square feet, of polyethylene, U.S.I. grade 203-2, having a nominal density of 0.916 and a melt index of 8.0. This lamination was then extrusion coated on the cellophane side with 26 pounds, per 3000 square feet, of polyethylene, U.S.I. grade 2032. The cellophane was prime coated on both sides with a dilute solution of polyethylene imine before combining with the polyethylene.

No. 2: A film of 50 gauge, heat-set, biaxially oriented polypropylene, Moplefane OTT from Montecatini of Italy, was extrusion laminated to 250 RS 1E cellophane (Saran-coated) from American Viscose Corp, with seven pounds, per 3000 square feet, of polyethylene, Monsanto grade MPE-70, having a nominal density of 0.919 and a melt index of 5.0. This lamination was then extrusion coated on the cellophane side with 24 pounds, per 3000 square feet, of polyethylene, Monsanto grade MPE-70. The cellophane was prime coated on both sides with a dilute solution of polyethylene imine before combining with the polyethylene.

No. 3: A film of 50 gauge, heat-set, biaxially oriented polypropylene, Moplefane OTT from Montecatini of Italy, was extrusion laminated to 250 XCP 6-05 cellophane from Du Pont, with five pounds, per 3000 square feet, of polyethylene, U.S.I. grade 2032, having a nominal density of 0.916 and a melt index of 8.0. This lamination was then extrusion coated on the cellophane side with 26 pounds, per 3000 square feet, of polyethylene, U.S.I. grade 203-2. The cellophane was prime coated on both sides with a dilute solution of polyethylene imine before combining with the polyethylene.

The laminated wrappers from Examples 1 and 2 above were used for the packaging of blocks of natural cheese, using a Hayssen Model RT wrapping machine. Air was flushed from the packages with carbon dioxide, using the gas flushing technique. A number of sealed packages with each type of wrapper were assembled in a corrugated shipping container.

For purposes of comparison, similar packages were prepared at the same time on the same machine, using the best avail-able commercial wrapper consisting of 50 gauge Saran-coated Mylar, coated on one side with two mils of polyethylene.

Packages of each of the wrappers from the examples, and the above control wrappers, assembled in the shipping container, were subjected to flexing stresses, intended to simulate actual handling and shipping stresses, by shaking the shipping container full of packages on a circular, syncoronous shaking table, having an amplitude of one inch, and a frequency of 210 cycles per minute. The presence of pinholes in each package wrapper was determined by applying slight air pressure to the package through a hypodermic needle, and inspect-ing thepackage for the origin of gas bubbles when held under water.

The shaking period used, and the resulting pinhole development from fiex cracking observed in the above tests are shown in the following table:

Flex crack failure of wrappers on shaken packages Another test which has been used to determine the relative effectiveness of different wrapping materials is to subject the packages to the same general shaking procedures as outlined in the above test and then store the packages under refrigerated conditions to determine the condition of the cheese at the end of a given period of time, say, four weeks. This test was run with the wrapper of Example No. 2, comparing the results with the Mylar wrapper, and it was found that the wrapper of this invention when used in twenty-three packages which were shaken for a four-hour period had only one package develop mold, represent 4% failure; whereas with the Mylar-polyethylene wrapper twenty-six packages shaken for a like period of four hours and then stored under identical refrigeration condition for the same period of time showed mold development in same period of time showed mold development in twenty of the twenty-six packages, or a failure of 77%.

The surprising superiority of our new Wrapping material has also been confirmed by an independent laboratory using other testing techniques in which it was established that the Mylar material failed after 15,000 cycles of flexing, whereas the wrapping material of this invention showed no signs of failure after 150,000 cycles of flexing.

Considering the fact that the laminate of this invention uses as base material the relatively fractile material cellophane, it is astounding that by this unique coacting combination of cellophane with other materials it is possible to obtain a wrapping material which shows a ten to one, or even greater, superiority over the strong and tough material Mylar with respect to flex cracking and pinhole development.

We claim:

1. An hermetically sealed food package of the type having nonconformed ends and characterized by its resistance to flex cracking and pinhole development for extended periods of time under severe handling conditions, said package consisting of a laminated wrapper having in sequential layers from exterior to interior, oriented polypropylene, polyethylene, Saran-coated cellophane, and polyethylene, and a food product within the package, said package containing an inert gas and being heat and pressure sealed.

2. An hermetically sealed food package of the type having nonconformed ends and characterized by its resistance to flex cracking and pinhole development for extended periods of time under severe handling conditions, said package consisting of a laminated wrapper of Saran-coated cellophane sandwiched between and bonded with an ethylene polymer to an outer layer of oriented polypropylene and bonded also to an inner layer of polyethylene, and a food product within the package.

3. An hermetically sealed food package of the type having nonconformed ends and characterized by its resistance to flex cracking and pinhole development for extended periods of time under severe handling conditions, said package consisting of a laminated wrapper having from exterior to interior, heat-set biaxially oriented polypropylene extrusion-laminated with polyethylene to Saran-coated cellophane which, in turn, is extrusion-coated with polyethylene on the cellophane side, and a perishable food product within the package, said package containing an inert gas and being heat and pressure sealed.

4. An hermetically sealed package as set forth in claim 1 in which the cellophane layer has a thickness of about .8 mil, the inside polyethylene coating has a thickness of at least about 1% mils, the outside polyethylene coating has a thickness of about .5 mil, and said exterior layer has a thickness of about .5 mil.

5. An hermetically sealed food package of the type having nonconformed ends and characterized by its resistance to flex cracking and pinhole development for extended periods of time under severe handling conditions, said package consisting of a laminated wrapper having Saran-coated cellophane, an inner layer of a heat-scalable ethylene polymer, and an outer layer of oriented polypropylene, said cellophane, heat-scalable ethylene polymer and polypropylene being bonded together with an ethylene polymer serving as a bonding agent between the polypropylene and the cellophane, said package containing a food product and being heat and pressure sealed.

References Cited by the Examiner UNITED STATES PATENTS 2,679,969 1/ 1954 Richter.

2,919,059 12/1959 Sporka 229-3.5 2,956,671 10/1960 Cornwell 206-46 3,033,707 5/1962 Lacy et al.

3,037,868 6/1962 Rosser 99171 A. LOUIS MONACELL, Primary Examiner. RAYMOND N. JONES, Assistant Examiner. 

2. AN HERMETICALLY SEALED FOOD PACKAGE OF THE TYPE HAVING NONCONFORMED ENDS AND CHARACTERIZED BY ITS RESISTANCE TO FLEX CRACKING AND PINHOLE DEVELOPMENT FOR EXTENDED PERIODS OF TIME UNDER SEVERE HANDLING CONDITIONS, SAID PACKAGE CONSISTING OF A LAMINATED WRAPPER OF SARAN-COATED CELLOPHANE SANDWICHED BETWEEN AND BONDED WITH AN ETHYLENE POLYMER TO AN OUTER LAYER OF ORIENTED POLYPROPYLENE AND BONDED ALSO TO AN INNER LAYER OF POLYETHYLENE, AND A FOOD PRODUCT WITHIN THE PACKAGE. 